Philes’ Forum – Winter 2019


By Vic Lucariello, Sr.

Hello Bimmerphiles! This time out I have a follow-up to my last column on AGM [Absorbent Glass Mat] batteries and an AGM-conversion story on my E30 M3. But first, a correction.

In the last Philes Forum, I reported that Odyssey Battery tells us the maximum operating temperature for their PC1200 AGM battery is 113F. I wrote that 113F is clearly above underhood operating temperatures. I meant to say that 113F is below underhood operating temperatures, so a PC1200 might not be suitable for an engine-compartment-mounted battery. I was inundated with a veritable Colorado Blizzard of emails taking me to task for this error. Hey, in 32 years of writing Philes’, this was my first error. NOT!

As part of the preparation for my last column, I also contacted another AGM-battery manufacturer, Optima. These batteries, with their distinctive cylindrical-shaped cells, are quite popular with racers. Optima says that their red-top automotive AGM batteries have a maximum operating temperature of 125F. Same ballpark as for the Odysseys.

After my successful AGM-battery installations in my hotrod and in Joanne’s 1995 [E36] 325is, I decided to put one in my E30 M3. [A disadvantage of having multiple vehicles is that one of them seemingly always needs a battery or tires. This time, three of them needed a battery.]

Given that the M3 is a 4-cylinder, I reasoned that it should not need as large and powerful a battery as does the six-cylinder 325is, so I selected an Odyssey Extreme PC925MJT. The Interstate MTP-91 battery I removed is rated at 700 CCA [Cold Cranking Amps] while the PC925MJT is rated at only 330 CCA. The MJ stands for metal jacket, not really necessary in this trunk -mount application. The T stands for traditional SAE top battery posts. Without the “T”, you don’t get battery posts, so keep this in mind. A PC925 is somewhat less expensive than a “MJ” or “T”, and I believe some Internet vendors might be taking advantage of this. Other reasons for selecting PC925MJT are that it precisely fits the width of the “plastic” battery tray in the M3 [same tray for all the trunk-mount-battery E30s] and it is about 13 pounds lighter than the Interstate. My M3 is a street-only ride, but for a track-driven car 13 pounds is a LOT of weight reduction.

Since the Odyssey battery does not have hold- down “feet” at the bottom of its case like the BCA [Battery Council of America] Group 91 batteries BMW specifies for the trunk-mount E30s, I had to make something to hold the battery down and prevent it from sliding fore and aft in the battery tray. I chose to use a piece of aluminum-alloy channel commonly available from industrial- supply houses such as McMaster-Carr. The problem was that I only needed a piece of channel less than a foot long and McMaster-Carr only sells the stuff in longer lengths. Oh well, so now I have some nice aluminum-alloy channel in stock.

I really hate to drill holes in automobile bodies unless it is absolutely necessary. This is because said holes need to be rust- proofed, and there ain’t no rustproofing like factory rustproofing. [You 2002 and 320i owners probably scoff at that statement.] On the M3 I was able to secure the battery-hold- down bolts [I used 8-millimeter threaded rod also available from McMaster-Carr] to the “plastic” battery tray by fashioning a couple of reinforcements affixed to the bottom of the tray, mimicking the factory reinforcements, and then mounting 8-mm “nut serts” through the reinforcements and tray bottom. See Photo #1, which shows the underside of the removed battery tray.

Photo #1 – Underside of reinforced battery tray.

One other problem to be solved was that the existing OE battery negative cable was too short to reach the new battery. I was able to source a seemingly very nice quality negative cable from Battery Cables USA. The cable is #2 AWG [American Wire Gauge], closely matching the metric wire gauge of the OE cable, and 12 inches long. Twelve inches was a little more than necessary, but a little longer is preferable to a little too short. BCA will make you a custom cable to your specs, but I chose the 12-inch, which was in stock.

The completed project, with the battery cover removed, is depicted in Photo #2. BMW’s “plastic” battery cover fits nicely over the new battery, yet another reason I chose the PC925MJT. The Group 91 battery specified for the E30 has provision for external venting, but this is not needed for the AGM battery. I put all the removed parts together and have them squirreled away in a safe place in case this smaller-than-stock battery does not work out. The M3 can easily be returned to stock configuration if necessary.

Photo #2 – Completed installation.

We typically have sub-zero-F overnight temperatures here in SW Colorado in January and February, and my M3 hibernates in my enclosed trailer during the nasty months. I am happy to report that when I started the M3 last week, the S14 engine cranked over vigorously and started right up. So time will tell if my choice of a lesser-CCA battery was wise.

That’s all for now, bimmerphiles. See you next time.

Anyone wishing to contribute to Philes’ Forum can contact me at I’m interested in comments, tech tips, repair /maintenance questions, repair horror stories, emissions inspection sagas, product evaluations, etc.

© 2019; V.M. Lucariello, P.E.

Philes’ Forum – Fall 2018


By Vic Lucariello, Sr.

Hello bimmerphiles! I recently got an unpleasant surprise when installing a new battery in Joanne’s 1995 325is [E36]. Might a similar surprise await you?

There exists controversy among bimmerphiles as to which 3-series is the best: E30, E36 or E46. You will note that I did not mention the E21, E90s or F30s. I guess your opinion will depend upon which model’s attributes are most important to you.

Anyway, my aforementioned surprise was due to a construction difference among the E30-36-46 cars. On the E30 [those with trunk- mount batteries] and E46, the battery is contained in a topless metal compartment on the right side of the luggage compartment. Indeed, on the E30 the battery sits in a “plastic” tray within this metal compartment. This is one of the nicest designs I have ever seen. So, on the E30 and E46, any damage due to decamped battery electrolyte will be readily apparent when the battery is removed, and said damage would hopefully be contained in the battery compartment. Not so on the E36!

Believe it or not, Joanne’s 200,000-mile 1995 E36 was on its second battery until recently. The BMW OE battery lasted fifteen years, and the Interstate replacement lasted until August of 2017. This might be a testament to my use of a battery maintainer whenever the car sits idle for more than a day.

In replacing the Interstate and cleaning up a bit of corrosion in the battery compartment, I noticed that, Hey!, the inboard side of the battery compartment is open to the spare-wheel compartment! I noticed this when I dropped a tool and it disappeared, only to be retrieved after the spare wheel was removed.

And that is when I got The Surprise.

Photos 1 and 2 depict the corrosion I found when I removed the spare wheel, which had been in place for years, having received only periodic air-pressure checks. Luckily, after removing the corrosion by liberally scrubbing with a Scotch Brite pad and Simple Green Industrial Cleaner and Degreaser [pH of about 9; you can also use a mixture of baking soda and water] I found the underlying metal to be OK. After flushing with water and drying overnight, the first-coat primed area is as shown in Photo #3.

Photo #1 – Surprise
Photo #2 – Shame on Vic
Photo #3 – Looking Better

After a second coat of primer and two coats of Rust-Oleum gloss black, things looked as shown in Photo #4: almost good as new. Incidentally, in the upper-right corner of the photo, you can see the bottom of the new battery, an Odyssey Extreme PC1200MJ AGM [Absorbent Glass Mat]. In an AGM battery the electrolyte is absorbed into fiberglass mats fitted between the cell plates. In a traditional flooded-cell leadacid automotive battery, the cell plates are suspended in liquid electrolyte, a mixture of sulfuric acid and water. So an AGM battery is less likely to spill electrolyte. Indeed, the Odyssey instructions indicate that the battery can be installed in any orientation except inverted. Other claimed advantages of AGM batteries are: longer service life, higher deep-discharge capability, slower self-discharge rate, higher vibration resistance, and higher cranking amperage for a given case size. A known disadvantage is higher cost, which may be offset by longer life. [The OE battery in Joanne’s E36 is a hard act to follow.] Possible disadvantages of AGMs are that they have a lower maximum operating temperature [some may not be suitable for an underhood environment], and [according to the Battery University Website] if your non-smart voltage regulator is set to charge at more than 13.8 volts, this could overcharge the battery on a long drive. The Odyssey Battery Technical Manual suggests a “float-charge” voltage of 13.6 volts [roughly equivalent to the required voltage- regulator setting], and a charging voltage of 14.7 volts, but does not directly address voltage-regulator setting.

I found this a bit confusing, so I contacted Odyssey battery. These folks have always responded promptly to my queries. Regarding temperature limitations, Odyssey says that the max operatingtemperature for the PC1200 battery is 113 F, clearly above underhood operating temperatures. For the metal-jacketed PC1200MJ, however, the maximum temperature is 176 F. For a trunk-mounted battery, I think the non-metal-jacket PC1200 would be OK, but for a few more dollars, I went with the PC1200MJ.

Photo #4 – Almost Good as New

Regarding charging voltage, the Odyssey Product Guide’s warranty section specifically states that the alternator should be set to provide between 14.0 and 14.7 volts, and if the charging system is not set within these limits, shortened battery life can be expected, as well as a voided warranty. This can be a problem on BMWs, some of which use a charging voltage lower than 14 volts [Forget the newer “smart” charging systems, where battery voltage is not held constant.]. The charging system on Joanne’s E36 runs at about 14.2 – 14.3 volts after things warm up, while my M3, which also has an Odyssey, runs at about 13.6 volts. So we shall see how things work out. Perhaps I should have read the fine print more thoroughly….

I chose the PC1200MJ because, while it has a lower cold-cranking- amperage rating than BMW specifies [540 vs. 700], the PC1200MJ is short enough not to interfere with the battery compartment’s “plastic” cover. Since the car is rarely if ever started in cold temperatures, I think that 540 cold-cranking amps should suffice. Again, we shall see. Odyssey does not offer a direct-replacement battery for the E36.

Evidently BMW believes that AGMs are superior batteries, as BMW has been installing them for some years now, especially in Bimmers with “smart” charging systems. I am interested in knowing what battery life your Bimmer experiences, regardless of whether it has an AGM battery. From reports I read on iATN, the International Automobile Technicians Forum, BMW battery life ain’t what it used to be.

That’s all for now, bimmerphiles. See you next time.

Anyone wishing to contribute to Philes’ Forum can contact me at I’m interested in comments, tech tips, repair /maintenance questions, repair horror stories, emissionsinspection sagas, product evaluations, etc.

© 2018; V.M. Lucariello, P.E.

Related Articles - Philes' Forum